1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device and a method of driving the same.
2. Discussion of the Related Art
Until recently, display devices have typically used cathode-ray tubes (CRTs). Presently, much effort is being expended to study and develop various types of flat panel displays, such as liquid crystal display (LCD) devices, plasma display panels (PDPs), field emission displays (FED), and electro-luminescence displays (ELDs), as a substitute for CRTs. In particular, these types of flat panel displays have been driven in an active matrix type display in which a plurality of pixels arranged in a matrix form are driven using a plurality of thin film transistors therein. Among the active matrix types of flat panel displays, liquid crystal display (LCD) devices and electroluminescent display (ELD) devices are widely used as monitors for notebook computers and desktop computers because of their high resolution, ability to display colors and superiority in displaying moving images.
In general, an LCD device includes two substrates that are spaced apart and face each other with a liquid crystal material interposed between the two substrates. The two substrates include electrodes that face each other such that a voltage applied between the electrodes induces an electric field across the liquid crystal material. Alignment of the liquid crystal molecules in the liquid crystal material changes in accordance with the intensity of the induced electric field in the direction of the induced electric field, thereby changing the light transmissivity of the LCD device. Thus, the LCD device displays images by varying the intensity of the induced electric field.
Recently, a vertical alignment (VA) mode LCD device is used to achieve a wide viewing angle.
FIG. 1 is a circuit diagram of a VA mode LCD device according to the related art, and FIG. 2 is a waveform view of a common voltage and a storage voltage supplied to a pixel of the LCD device of FIG. 1.
As shown in FIG. 1, the related art LCD device includes a plurality of gate lines G(n−1) to G(n+1) that are extended along a first direction, and a plurality of data lines D(m−1) to D(m+1) that are extended along a second direction and crossing the gate lines.
A plurality of pixels are arranged in a matrix form. Each pixel is connected to the corresponding one of the gate lines G(n−1) to G(n+1) and the corresponding one of the data lines D(m−1) to D(m+1). Each pixel includes a thin film transistor TFT, a liquid crystal capacitor Clc and a storage capacitor Cst. One electrode of the liquid crystal capacitor Clc is connected to the thin film transistor TFT, and the other electrode of the liquid crystal capacitor Clc is supplied with a common voltage Vcom. One electrode of the storage capacitor Cst is connected to the thin film transistor TFT, and the other electrode of the storage capacitor Cst is supplied with a storage voltage Vst. The storage voltage Vst determines an amount of a voltage stored in the pixel.
The related art LCD device is driven in a method wherein two pixels arranged adjacent along one of the data lines D(m−1) to D(m+1) and connected to the same one of the gate lines G(n−1) to G(n+1), as shown with a dashed box in FIG. 1, are supplied with the same data voltage. The two pixels supplied with the same data voltage constitute a pixel unit PXL.
Referring to FIG. 2, a DC (direct current) common voltage Vcom and an AC (alternating current) storage voltage Vst are supplied to each pixel. The storage voltage Vst has a specific frequency and alternates with respect to the common voltage Vcom. A waveform of the storage voltage Vst supplied to one pixel of the pixel unit PXL is opposite to a waveform of the storage voltage Vst supplied to the other pixel of the pixel unit PXL.
Since the storage voltages Vst having the different phase are supplied to the two pixels of the pixel unit PXL, the two pixels have different voltages stored. Accordingly, in the two pixels supplied with the same data voltage, a rotational angle difference of liquid crystal molecules is generated. By this difference, a viewing angle of the LCD device is improved.
However, the related art LCD device has some problems. A storage line, which transfers the storage voltage and is formed at the same step of forming the data line or the gate line, has a resistance load and a capacitance load. Such loads of the storage line cause a drop in the storage voltage along the storage line path. In particular, since the storage voltage has an AC waveform, the storage voltage drop appears remarkably. Accordingly, the storage voltage desired is not supplied to the pixel as the pixel gets closer to the end of the storage line. Therefore, improvement of the viewing angle is reduced and a display quality is degraded.